1. Field of the Invention
This invention relates to precursors which will undergo elimination reactions to produce iminoquinones and quinones in situ after cleavage of a blocking group, and more particularly to para-hydroxyphenylhydrazine and its derivatives and their use as in situ precursors of iminoquinones and quinones.
2. Description of the Prior Art
Quinones and iminoquinones have many uses in biological systems as a result of their toxicity. The simplest quinone, p-benzoquinone, for example, was shown to be a potent bactericidal substance against Salmonella typhosa as early as 1911. Many other quinones and iminoquinones are also known to have biological activity. For example, chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) has marked antifungal properties, while blue-green algae are inhibited by 2,3-dichloro-1,4-naphthoquinone. When used in this application, the term "quinones" will refer generically to all the quinones whatever the number of rings on the substituents and the term "iminoquinones" will similarly refer to all iminoquinones, unless otherwise specified.
Nitrogen analogues of the quinones (i.e., iminoquinones) have not been as extensively studied as the quinones themselves, perhaps because iminoquinones hydrolyze rapidly in aqueous solutions to the corresponding quinones. Thus, they have been difficult to study in biological systems because of the uncertainty as to what the reactive species is, a quinone or an iminoquinone. This may not be important in biological systems since iminoquinones appear to exhibit roughly similar reactivity to quinones in the typical reactions that both undergo (both act as oxidizing agents and electrophiles). Iminoquinones have been prepared and tested for biological activity, for example in Hodnett et al, J. Med. Chem. 21, 11-16 (1978) which is hereby incorporated by reference, and have been shown to exhibit cytotoxic activity.
The toxicity of quinones and iminoquinones, and hence their biological activity, is caused by their high degree of reactivity, particularly with nucleophiles, such as the --SH group of cysteine and other biological thiols. However, this very reactivity works against them since they often react with other nucleophiles before reaching the site in the biological system where their activity is desired.
Accordingly, there have been attempts to use precursors of quinones and iminoquinones in order to produce the reactive compounds in situ. For example, p-benzohydroquinone has been used to generate p-benzoquinone in situ to prevent phage (viral) infections from proliferating in tissue cultures. However, this oxidation reaction to form the quinone is itself not very selective for biological systems, since oxidation can occur on standing in air. More desirable would be a precursor which forms the reactive quinone or iminoquinone selectively at a site of biological activity, e.g., an enzyme active site. In such a case the quinone would be generated only at sites of biological activity where reaction was desired. Although quinones and some iminoquinones have been extensively studied and reviewed, for example in J. L. Webb, "Enzyme and Metabolic Inhibitors", V.III, Academic Press, New York and London (1966), pp. 421-594, which is hereby incorporated by reference, no such precursors of general utility have previously been known.
There is however, a known reaction in which an iminoquinone is generated in situ in a biological system, although it represents only a minor side reaction rather than a general case. Researchers investigating the toxicity of N-(4-hydroxyphenyl)acetamide, also known as acetaminophen, discovered that about 2% of the acetaminophen was oxidized in liver cells (hepatocytes) to an N-hydroxylated compound that could lose a water molecule to form N-acetyl-p-iminobenzoquinone. ##STR2## This iminoquinone was shown to be responsible for the toxic effects in the liver (1. Gillette, J. R. et. al.: "Biochemical Mechanism of Drug Toxicity" in Ann. Rev. of Pharmacology. 14:271 (1974) 2. Mitchell, J. R. et. al.: Handb. Exp. Pharmacol. 28/3 (1975) p. 383. 3. Potter, W. J. et al.: Pharmacology 12:129 (1974)).
Other investigators showed that by replacing the hydrogen of the phenolic hydroxyl group with a sulfate that could later be enzymatically cleaved, the intermediate N-hydroxylated amide could be isolated and studied (Gemborys, M. W. et al.: J. Med. Chem. 21:649-652 (1978)).
However, this reaction sequence does not provide a general method of producing quinones or iminoquinones in situ in other biological systems since it requires an initial oxidation by hepatocytes.